bioe 109 summer 2009 lecture 11-part ii speciation
Post on 19-Dec-2015
218 views
TRANSCRIPT
![Page 1: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/1.jpg)
BIOE 109Summer 2009
Lecture 11-Part IISpeciation
![Page 2: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/2.jpg)
What is speciation?
![Page 3: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/3.jpg)
What is speciation?
• in Darwin’s words, speciation is the “multiplication of species”.
![Page 4: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/4.jpg)
What is speciation?
• in Darwin’s words, speciation is the “multiplication of species”.
• according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms.
![Page 5: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/5.jpg)
What is speciation?
• in Darwin’s words, speciation is the “multiplication of species”.
• according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms.
• the barriers may act to prevent fertilization – this is pre-zygotic isolation.
![Page 6: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/6.jpg)
What is speciation?
• in Darwin’s words, speciation is the “multiplication of species”.
• according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms.
• the barriers may act to prevent fertilization – this is pre-zygotic isolation.
• may involve changes in location or timing of breeding, or courtship.
![Page 7: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/7.jpg)
What is speciation?
• in Darwin’s words, speciation is the “multiplication of species”.
• according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms.
• the barriers may act to prevent fertilization – this is pre-zygotic isolation.
• may involve changes in location or timing of breeding, or courtship.
• barriers also occur if hybrids are inviable or sterile – this is post-zygotic isolation.
![Page 8: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/8.jpg)
Modes of Speciation
![Page 9: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/9.jpg)
Modes of Speciation
1. Allopatric speciation
![Page 10: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/10.jpg)
Modes of Speciation
1. Allopatric speciation
• reproductive isolation occurs in complete geographic isolation.
![Page 11: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/11.jpg)
Modes of Speciation
1. Allopatric speciation
• reproductive isolation occurs in complete geographic isolation (no gene flow).
![Page 12: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/12.jpg)
Geographic isolation can rise from dispersal or vicariance
![Page 13: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/13.jpg)
Modes of Speciation
1. Allopatric speciation
• reproductive isolation occurs in complete geographic isolation (no gene flow).
Example: Hawaiian Drosophila
![Page 14: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/14.jpg)
HawaiianDrosophila
D. suzukii
D. microthrix
D. nigribasis
![Page 15: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/15.jpg)
Speciation by island-hopping
![Page 16: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/16.jpg)
Modes of Speciation
2. Parapatric speciation
![Page 17: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/17.jpg)
Modes of Speciation
2. Parapatric speciation
• reproductive isolation occurs without complete geographic isolation (some gene flow).
![Page 18: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/18.jpg)
Modes of Speciation
2. Parapatric speciation
• reproductive isolation occurs without complete geographic isolation (some gene flow).
Example: ring species of salamanders (Ensatina) in CA
![Page 19: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/19.jpg)
Ensatina salamanders
![Page 20: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/20.jpg)
Ring species – evidence for parapatric speciation
![Page 21: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/21.jpg)
Ring species – evidence for parapatric speciation
![Page 22: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/22.jpg)
Modes of Speciation
3. Sympatric speciation
![Page 23: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/23.jpg)
Modes of Speciation
3. Sympatric speciation
• reproductive isolation evolves with complete geographic overlap.
![Page 24: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/24.jpg)
Modes of Speciation
3. Sympatric speciation
• reproductive isolation evolves with complete geographic overlap.
Example: the apple maggot fly, Rhagoletis pomonella?
![Page 25: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/25.jpg)
Apple maggot fly Hawthorn fly
Speciation due to host specialization in this case
![Page 26: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/26.jpg)
Original population
Initial step of speciation
Evolution of reproductiveisolation
Allopatric peripatric parapatric sympatric
Modes of speciation: summary
Barrier formation
Newniche
Newniche
Geneticpolymorphism
In isolation In isolation In adjacentniche
Within thepopulation
![Page 27: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/27.jpg)
What evolutionary processes are involved in speciation?
![Page 28: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/28.jpg)
What evolutionary processes are involved in speciation?
1. Natural selection
![Page 29: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/29.jpg)
What evolutionary processes are involved in speciation?
1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites).
![Page 30: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/30.jpg)
What evolutionary processes are involved in speciation?
1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites).
2. Sexual selection
![Page 31: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/31.jpg)
What evolutionary processes are involved in speciation?
1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites).
2. Sexual selection
• both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila).
![Page 32: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/32.jpg)
What evolutionary processes are involved in speciation?
1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites).
2. Sexual selection
• both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila).
• sexual antagonistic selection too!
![Page 33: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/33.jpg)
Male-male competition in Hawaiian Drosophila
Establish territoryOn a lek by head butting
Fight over displayTerritory by grappling
![Page 34: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/34.jpg)
What evolutionary processes are involved in speciation?
3. Random genetic drift
![Page 35: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/35.jpg)
What evolutionary processes are involved in speciation?
3. Random genetic drift
• may involve founder effects and genetic bottlenecks.
![Page 36: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/36.jpg)
What evolutionary processes are involved in speciation?
3. Random genetic drift
• may involve founder effects and genetic bottlenecks.
• alleles that are neutral in one environment may not be neutral in another!
![Page 37: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/37.jpg)
Some generalities
1. The magnitude of pre-zygotic and post-zygotic isolation both increase with the time.
![Page 38: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/38.jpg)
Some generalities
1. The magnitude of prezygotic and postzygotic isolation both increase with the time.
• in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve.
![Page 39: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/39.jpg)
Some generalities
1. The magnitude of prezygotic and postzygotic isolation both increase with the time.
• in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve.
• in marine bivalves, it may take 4 to 6 million years!
![Page 40: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/40.jpg)
Some generalities
1. The magnitude of prezygotic and postzygotic isolation both increase with the time.
• in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve.
• in marine bivalves, it may take 4 to 6 million years!
2. Among recently separated groups, pre-zygotic isolation is generally stronger than post-zygotic isolation.
![Page 41: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/41.jpg)
Some generalities
3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex.
![Page 42: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/42.jpg)
Some generalities
3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex.
• for example, D. simulans and D. mauritiana female hybrids are completely viable yet male hybrids are completely sterile!
![Page 43: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/43.jpg)
Some generalities
3. In the early stages of speciation, hybrid sterility or inviability is almost always seen in the heterogametic sex.
• for example, D. simulans and D. mauritiana female hybrids are completely viable yet male hybrids are completely sterile!
• this is called Haldane’s rule.
J.B.S. Haldane (1892-1964)
![Page 44: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/44.jpg)
What causes post-zygotic isolation?
![Page 45: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/45.jpg)
What causes postzygotic isolation?
• the underlying mechanism is called Dobzhansky-Muller incompatibility:
![Page 46: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/46.jpg)
Dobzhansky and Muller were incompatible!
“Balanced” school
“Classical” school
![Page 47: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/47.jpg)
What causes postzygotic isolation?
• the underlying mechanism is called Dobzhansky-Muller incompatibility:
Ancestral Pop: A1A1B1B1
![Page 48: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/48.jpg)
What causes postzygotic isolation?
• the underlying mechanism is called Dobzhansky-Muller incompatibility:
Ancestral Pop: A1A1B1B1
Derived Pops: A2A2B1B1 A1A1B2B2
![Page 49: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/49.jpg)
What causes postzygotic isolation?
• the underlying mechanism is called Dobzhansky-Muller incompatibility:
Ancestral Pop: A1A1B1B1
Derived Pops: A2A2B1B1 A1A1B2B2
Hybrids: A1A2B1B2 fitness
![Page 50: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/50.jpg)
Differences between plant and animal speciation
![Page 51: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/51.jpg)
Differences between plant and animal speciation
• in plants, polyploidization is a major mode of speciation.
![Page 52: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/52.jpg)
Differences between plant and animal speciation
• in plants, polyploidization is a major mode of speciation.
• polyploidization refers to the retention of extra sets of chromosomes (i.e., tetraploids, octoploids, etc.)
![Page 53: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/53.jpg)
Differences between plant and animal speciation
• in plants, polyploidization is a major mode of speciation.
• polyploidization refers to the retention of extra sets of chromosomes (i.e., tetraploids, octoploids, etc.)
• there are two types of polyploids: autopolyploids and allopolyploids.
![Page 54: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/54.jpg)
Differences between plant and animal speciation
• autopolyploids add chromosomal sets from the same species:
![Page 55: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/55.jpg)
Differences between plant and animal speciation
• autopolyploids add chromosomal sets from the same species:
Species 1 x Species 1 Species 2 (2N = 4) (2N = 4) (4N = 8)
![Page 56: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/56.jpg)
Differences between plant and animal speciation
• autopolyploids add chromosomal sets from the same species:
Species 1 x Species 1 Species 2 (2N = 4) (2N = 4) (4N = 8)
• allopolyploids combine chromosomal sets from different species:
![Page 57: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/57.jpg)
Differences between plant and animal speciation
• autopolyploids add chromosomal sets from the same species:
Species 1 x Species 1 Species 2 (2N = 4) (2N = 4) (4N = 8)
• allopolyploids combine chromosomal sets from different species:
Species 1 x Species 2 Species 3 (2N = 4) (2N = 6) (2N = 10)
![Page 58: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/58.jpg)
Secondary contact and reinforcement
![Page 59: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/59.jpg)
Secondary contact and reinforcement
• secondary contact occurs when two formerly allopatric populations meet.
![Page 60: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/60.jpg)
Secondary contact and reinforcement
• secondary contact occurs when two formerly allopatric populations meet.
Three outcomes are possible:
![Page 61: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/61.jpg)
Secondary contact and reinforcement
• secondary contact occurs when two formerly allopatric populations meet.
Three outcomes are possible:
1. No interbreeding occurs
![Page 62: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/62.jpg)
Secondary contact and reinforcement
• secondary contact occurs when two formerly allopatric populations meet.
Three outcomes are possible:
1. No interbreeding occurs
• isolating mechanisms in place – speciation completed.
![Page 63: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/63.jpg)
Secondary contact and reinforcement
• secondary contact occurs when two formerly allopatric populations meet.
Three outcomes are possible:
1. No interbreeding occurs
• isolating mechanisms in place – speciation completed.
2. Introgression
![Page 64: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/64.jpg)
Secondary contact and reinforcement
• secondary contact occurs when two formerly allopatric populations meet.
Three outcomes are possible:
1. No interbreeding occurs
• isolating mechanisms in place – speciation completed.
2. Introgression
• no isolating mechanisms in place – populations merge completely.
![Page 65: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/65.jpg)
Secondary contact and reinforcement
3. Partial interbreeding occurs
![Page 66: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/66.jpg)
Secondary contact and reinforcement
3. Partial interbreeding occurs
• some isolating mechanisms in place – a hybrid zone forms (but hybrids are less fit).
![Page 67: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/67.jpg)
Secondary contact and reinforcement
3. Partial interbreeding occurs
• some isolating mechanisms in place – a hybrid zone forms (but hybrids are less fit).
• reinforcement should occur to “complete” the process by the evolution of additional pre-zygotic barriers.
![Page 68: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/68.jpg)
Evidence for reinforcement in Drosophila
![Page 69: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/69.jpg)
Evidence for reinforcement in Drosophila
• Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric.
![Page 70: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/70.jpg)
Evidence for reinforcement in Drosophila
• Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric.
For each species pair they estimated:
![Page 71: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/71.jpg)
Evidence for reinforcement in Drosophila
• Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric.
For each species pair they estimated:
1. The degree of pre-mating isolation from mate choice experiments.
![Page 72: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/72.jpg)
Evidence for reinforcement in Drosophila
• Coyne & Orr (1997) compared sister species of Drosophila that were either allopatric or sympatric.
For each species pair they estimated:
1. The degree of premating isolation from mate choice experiments.
2. The degree of genetic divergence using allozymes.
![Page 73: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/73.jpg)
Evidence for reinforcement in Drosophila
![Page 74: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/74.jpg)
Ecological speciation in sticklebacks
![Page 75: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/75.jpg)
Ecological speciation in sticklebacks
![Page 76: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/76.jpg)
Ecological speciation in sticklebacks
![Page 77: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/77.jpg)
Ecological speciation in sticklebacks
![Page 78: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/78.jpg)
1. Colonization by marine stickleback ~10,000 years ago
Ecological speciation in sticklebacks
![Page 79: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/79.jpg)
1. Colonization by marine stickleback ~10,000 years ago
2. Adaptation to freshwater environment
Ecological speciation in sticklebacks
![Page 80: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/80.jpg)
1. Colonization by marine stickleback ~10,000 years ago
2. Adaptation to freshwater environment
3. Secondary invasion by marine stickleback
Ecological speciation in sticklebacks
![Page 81: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/81.jpg)
3. Secondary invasion by marine stickleback
Ecological speciation in sticklebacks
![Page 82: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/82.jpg)
3. Secondary invasion by marine stickleback
4. Evolution of limnetic and benthic sticklebacks
Ecological speciation in sticklebacks
![Page 83: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/83.jpg)
Evidence for secondary invasion hypothesis
![Page 84: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/84.jpg)
Evidence for secondary invasion hypothesis
1. Only low elevation lakes possess limnetic and benthic species pairs.
![Page 85: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/85.jpg)
Evidence for secondary invasion hypothesis
1. Only low elevation lakes possess limnetic and benthic species pairs.
2. Cores from lakes with limnetic and benthic species pairs show evidence of salt water influx (e.g, clams, etc.).
![Page 86: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/86.jpg)
Evidence for secondary invasion hypothesis
1. Only low elevation lakes possess limnetic and benthic species pairs.
2. Cores from lakes with limnetic and benthic species pairs show evidence of salt water influx (e.g, clams etc.).
3. Higher elevation lakes have neither limnetic and benthic species pairs nor evidence of salt water influx.
![Page 87: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/87.jpg)
What types of genes are involved in speciation?
Example: desat-2 in D. melanogaster
![Page 88: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/88.jpg)
What types of genes are involved in speciation?
Example: desat-2 in D. melanogaster
• D. melanogaster has radiated out of Africa with humans and lives all over the world (in our garbage cans).
![Page 89: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/89.jpg)
What types of genes are involved in speciation?
Example: desat-2 in D. melanogaster
• D. melanogaster has radiated out of Africa with humans and lives all over the world (in our garbage cans).
• female flies from Africa (A) possess a different cuticular hydrocarbon than cosmopolitan females (C).
![Page 90: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/90.jpg)
What types of genes are involved in speciation?
Example: desat-2 in D. melanogaster
• D. melanogaster has radiated out of Africa with humans and lives all over the world (in our garbage cans).
• female flies from Africa (A) possess a different cuticular hydrocarbon than cosmopolitan females (C).
• difference due to a different position of a single double bond.
![Page 91: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/91.jpg)
2. desat-2 in D. melanogaster
• the desat-2 mutation also affects mate choice.
![Page 92: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/92.jpg)
2. desat-2 in D. melanogaster
• the desat-2 mutation also affects mate choice.
• when A females are placed with A and C males, they only mate with the former.
![Page 93: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/93.jpg)
2. desat-2 in D. melanogaster
• the desat-2 mutation also affects mate choice.
• when A females are placed with A and C males, they only mate with the former.
• this modified hydrocarbon affects female smell – in effect they wear a different “perfume”.
![Page 94: BIOE 109 Summer 2009 Lecture 11-Part II Speciation](https://reader034.vdocuments.mx/reader034/viewer/2022042615/56649d3b5503460f94a15d2b/html5/thumbnails/94.jpg)
2. desat-2 in D. melanogaster
• the desat-2 mutation also affects mate choice.
• when A females are placed with A and C males, they only mate with the former.
• this modified hydrocarbon affects female smell – in effect they wear a different “perfume”.
• the A females are not courted very intensely by C males.